Living cells are surrounded by an outer cell membrane that restricts the movement of ions and solutes between the cell interior and the exterior of the cell. Changes in the electrical activity of cell membranes can reflect the biophysical state of the cells and further reflect underlying physiological and biochemical processes occurring within the cell, as well as biophysical changes occurring at the surface of the cell or in the cell membrane. Electrical devices and apparatus for the measurement of electrical impedance can be used to detect the state of the electrophysiological activity of living cells and their cell membranes.
Cell-electrode impedance sensing and cell substrate electrical impedance sensing are two related electrical measurements that are based on the application of a small alternating current (AC) electrical signal to probe the value of the impedance of sensor electrodes immersed in a conductive medium. Living cells can attach and grow on the surface of the sensor electrodes and can alter the electric field between electrodes causing a change in the electrical impedance that can be detected by the sensor electrodes. The measurement of impedance by the sensor can reflect the electrophysiological state of the cell and can allow the biophysical properties of the cell to be monitored.